ALMATY, Kazakhstan — Iran and six world powers failed to reach agreement Saturday on an approach to reducing fears that Tehran might use its nuclear technology to make weapons, with the EU’s foreign policy chief declaring that the two sides “remain far apart on substance.” Expectations that the negotiations were making progress rose as an afternoon session was extended into the evening. But comments by the two sides made clear that they failed to make enough headway to qualify the meeting as a success. “What matters in the end is substance, and ... we are still a considerable distance apart,” Catherine Ashton, the European Union’s head of foreign policy, told reporters at the end of the two-day talks. Ashton said negotiators would now consult with their capitals. She made no mention of plans for a new meeting — another sign that the gap dividing the two sides remains substantial. Chief Iranian negotiator Saeed Jalili spoke of “some distance between the positions of the two sides.” He suggested Iran was ready to discuss meeting a key demand of the other side — cutting back its highest-grade uranium enrichment production and stockpile — but only if the six reciprocated with concessions far greater than they are now willing to make. The six are the United States, Russia, China, Britain, France and Germany.